"Underachievement" is a well-established educational research field. However, both longitudinal and interdisciplinary studies on the interplay between individuals' learning potential and educational attainment are rare, as are analyses of life course consequences of underachievement. This psychological, sociological, and economic longitudinal study aims to contribute to our knowledge of social disparities in the processes of discovering youths' learning potential-and its development-in families, schools, and vocational training markets. We are less interested in replicating well-researched variations in the achievement-ability-relationship between social classes. Instead, we focus on within-group differences, both during schooling (within social classes) and during transitions from school to vocational training and labor markets (within educational groups). Such intra-group differences would reveal whether underachievement of children from lower-class and higher-class families is generated by similar or different mechanisms, and whether the mechanisms common to all social classes differ in strength in generating underachievement. Our unique data collection would allow us to investigate intra-group variance, even the crucial relationships between achievement, ability, and personality. In addition, a novel decomposition of family background will be coupled with a multidimensional life course approach examining interaction between youth and their siblings, partners, and parents.